What does moving from a 150 watt amp to a 400 watt amp get you?

I think you have an excellent amp and I'd leave it at that. 

You need a lot of power to significantly increase volume. Doubling the volume requires 10x the power. Without doing the math, volume wise you may gaine around 4 dB going from 150 to 400. ( 150 to 300 is 3 dB). 

But  you may need a lot of current, which your amps should have. 

Best,


Erik 

I’ve seen others say that these speakers need to be driven by 400 Watts to get them to sound their best.

If you really need 400 watts to make a speaker work, in a nutshell the efficiency of the speaker is borderline criminal. The reason why is simple- if you want an amp that really sounds like really real music, you can count on one hand the number of amps that make that kind of power as well. With almost any technology, the larger amps tend to be less musical. The reason is that First Watt you hear so much about- while that is a bit of a generalization, the fact is that many amps at lower power levels actually make a fair amount of distortion. So if you have a 400 watt amp as opposed to a 150 watt amp, that distortion level might be a bit more audible.

How this manifests is that you loose low level detail- and there is a tendency to turn it up to try to get more impact.

If you're not clipping your amp right now, I'd hang on to it!

An auxiliary space heater.

miles-train, 
the difference in watts are just numbers. you will notice that the same number of watts in one unit is NOT the same as the same number or watts in another amp. A good example are Naim amps, whose 50 watts are more powerful than many manufacturers that tout 100watts. Its just a conservative estimate of wattage for Naim. and many times, manufacturers are describing power in terms of amps or dB of gain. 

the point I want to make is about gain, different than watts or power.

Maybe an analogy: if 150 watts compared to 400 watts was like 5 gallons of gas in your car compared to 15 gallons of gas in your car. But you have the choice of the amount of gas octane you put in your tank.

In CA, we have 87, 89, or 91 octane. So the octane will give you boost, speed, and run a lil hotter. Meaning that the gain of the 150w/5 gallons vs 400w/15 gallons can be different. you might have high gain (91 octane) with 150 watts or low gain (87 octane). Same for the 400w amp Each amp manufacturer is different, and they try to establish an even amount of gain that sound pretty good at low or high volume levels.

But generally speaking, a 400w unit will give you more gain at lower volume levels than 150w amp. The point is that the higher the gain, the better your stereo will sound at lower volumes, b/c the 91 octane will distribute the energy to more of the hi and low frequencies and tend to give more of a "live" sound. doing this will take some energy from the mids, since the energy is spread out (think of a bell curve here) to the right and left extremes (the "bell" in the middle lowers). 

Last, I would try to explain this by using the Easter Electric BBA, Booster Buffer amp. It is a small unit, has 3 tubes and a transformer. Only 2 knobs on the front: VOLUME AND GAIN. in 10 years of audiophile, it is the most valuable unit I have had in terms of learning how to control sound through my speakers, and how to mitigate bad recordings and get to sound good. e.g. if I am playing a CD with too much gain ("loudness wars"), I reduce the gain and match to a volume that sounds good. If I am playing a poorly recorded or old LP with low gain or flat dynamics, I will turn up the gain to give better hi/lo dynamics and breath new life into it. 

I know this doesn't give a concrete answer, but I'm hoping the theory will help you figure out what will work best for you.Last, I dont know if you are familier with SimAudio, but they are know for having strong, solid power from amps (and gain, but not too much). In that respect, they are similar to the Naim amps referred to above.